Questions About This Earthquake

Hey, so i aquired a super oldschool Earthquake amp, as shown in the picture. It is an Earthquake PA-4020 UHC. It says 4 x 20 Rms @ 4 Ohms. This guy is ungodly larger than any other amp ive seen and i was wondering if somebody whose a veteran would be able to tell me some more about this amp. Like when was it released for sale originally, for how much, whats the output, and what is it worth today. I would greatly appreciate it, thanks!